This invention relates to turbochargers for supplying relatively high pressure charge air to an internal combustion engine. More specifically, this invention relates to an improved turbocharger construction including control means for controlling turbocharger boost pressures in accordance with engine operating parameters such as speed and load.
Turbochargers are well known in the prior art, and typically comprise a turbine wheel and a compressor wheel mounted on a common shaft and carried within isolated turbine and compressor housings, respectively. The turbine housing includes a gas inlet and a gas outlet, and is coupled to the exhaust gas manifold of a combustion engine for circulation of the exhaust gases through the turbine housing to rotatably drive the turbine wheel. In turn, the turbine wheel rotatably drives the compressor wheel which comprises ambient charge air, and supplies the compressed air to the intake manifold of the engine.
Turbocharged engines are highly advantageous when compared with conventional naturally aspirated engines in that substantially denser air is delivered to the combustion chamber or cylinders of the engine. This increased air density enables the engine to operate at substantially higher performance levels and with greater efficiency. However, with many combustion engines, it is desirable to limit the maximum pressure, or boost, at which the charge air is delivered to the engine. That is, particularly at relatively high speed or load conditions, many turbochargers are capable of delivering charge air to the engine at pressures substantially greater than the engine or the turbocharger can withstand. Similarly, at relatively low speed or load conditions, the turbocharger output is often below a minimum desired pressure level. In this regard, the prior art includes a wide variety of valves and other pressure control devices and methods designed to adjust the turbocharger boost pressure as a function of predetermined engine operating conditions.
One method for improving turbocharger boost pressure at relatively low engine speed or load conditions has been to provide a divided turbine housing. That is, particularly for use with a multiple cylinder internal combustion engine, a divided turbine housing may be used having two generally identical turbine inflow volute passages each providing flow communication with the turbine wheel. See, for example, U.S. Pat. No. 3,292,364. The two volute passages are coupled to different ones of the engine cylinders so that the engine exhaust gas flow is divided into a pair of substantially similar pulsating gas streams. The pulse effect of the exhaust gases is particularly pronounced at low speed or load operation to yield an improved turbocharger boost pressure when compared with conventional non-divided turbine housings. However, such divided turbine housings are not designed to overcome the problem of turbocharger overboost when the engine is operated at relatively high speeds or loads.
Many control devices have been proposed for limiting maximum turbocharger boost pressure, and thereby controlling turbocharger overboost. Some of these devices are designed for use with a divided turbine housing, and comprise a coupling of the volute passages to a common exhaust stream. A valve is provided for variably opening and closing one of the volute passages to thereby adjust the gas flow characteristics. See, for example, U.S. Pat. No. 3,270,495. Devices of this type do not, however, take advantage of the gas flow pulse effect of true divided housing operation since the volute passages do not pass equal and balanced gas flows under all operations and conditions. Other similar prior art devices include movable flap valves for inversely adjusting the gas flow in a pair of volute passages to alter the gas flow characteristics. See, for example, U.S. Pat. Nos. 3,557,549 and 3,614,249. However, these devices also fail to achieve equal, balanced gas flow at all times, and thereby do not provide the pulsation advantages of a true divided housing operation. Still other prior art devices provide adjustable gas flow characteristics by means of relatively complicated movable vanes. See, for example, U.S. Pat. No. 3,313,518.
This invention overcomes the problems and disadvantages of the prior art by providing an improved turbocharger having a divided turbine housing, and including a valve and supplemental control volutes for adjustably controlling the gas flow rate within the turbine housing in accordance with engine operating parameters.